• Question: Why is pluto not a planet anymore and is considered as a dwarf planet?

    Asked by popthebottle to Meeks, Pete, Stephen, Steve, Tom on 21 Jun 2010 in Categories: .
    • Photo: Marieke Navin

      Marieke Navin answered on 18 Jun 2010:

      Oh I know a few years ago they decided little Pluto was too small to be a planet and it’s just one of the cold freezing objects out there…there’s so much small frozen stuff out there. Poor Pluto

    • Photo: Tom Hartley

      Tom Hartley answered on 18 Jun 2010:

      To me, this is a bit like another question we had: “why is an orange called an orange, when a banana is not called a yellow?”. The words we use (such as planet) don’t signify anything unless we say they do. The IAU who decide how we identify astronomical objects decided they couldn’t keep calling Pluto a planet (mainly, I think, because they had found so many other things which would fit the description just as well). So they decided to change the definition. But nothing about Pluto has changed, and it is still the same thing whatever we call it.

    • Photo: Stephen Curry

      Stephen Curry answered on 19 Jun 2010:

      Pluto did a bad thing and was rightly punished by the Council of the Planets. Naughty Pluto!

      Seriously I’m not sure. I think it is just too small, compared to the other planets and compared to other bits of rock floating out there that aren’t called planets either.

      I know it has upset some scientists but part of science it being precise in your definitions and classifications of what things are. It may be shame to have 8 planets now rather than 9, but Pluto is still there (as are many other interesting things in our solar system apart from the planets).

    • Photo: Pete Edwards

      Pete Edwards answered on 21 Jun 2010:

      As telescopes have improved we have begun to see many new objects orbiting our sun, some of them about the size of Pluto or even bigger. So the question posed by astronomers was – do we just keep increasing the number of major planets that orbit our sun every time we discover a new one and keep re-writing the textbooks every few years?
      It was decided that a definition of what a planet is was needed. This definition was set in 2006 by the International Astronomical Union (IAU). It states that in the Solar System a planet is a celestial body that:
      1. Is in orbit around the Sun
      2. Has sufficient mass that its own gravity pulls it into a nearly round shape
      3. Has enough gravity to attract all the other bits of rock etc. and “cleared the neighbourhood” around its orbit.
      Pluto doesn’t fit this definition so is now a ‘dwarf planet’ or ‘plutoid’.

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